Skid steered all terrain vehicle

ABSTRACT

A skid steered all terrain vehicle (ATV), comprising two driving units for the wheels or tracks on both sides of the vehicle and a differential steering device with a differential gear, wherein the ATV is a light ATV (LATV) and wherein the differential steering device is designed to produce a defined differential speed of the two drive units of the vehicle related to the steering angle of the steering device regardless to the surface condition where the vehicle is driving, whereby an additional steering drive acts on the differential gear.

TECHNICAL FIELD

The present invention pertains to a skid steered All Terrain Vehicle(ATV), comprising a steering device, whereby the ATV has skid steeredwheels or endless tracks, and the steering device comprises adifferential gearbox.

BACKGROUND OF THE INVENTION

ATV's are existing in different layouts and with different drive- andsteering systems. There are mainly two categories how steering can beeffectuated on such vehicles.

In the first and most common category of such vehicles, the vehicles aresteered by at least two wheels, which are pivoting horizontally around avertical pivot point. These wheels are connected either mechanically byrods or gears to a steering wheel or a handlebar. The driver turns thehandlebar or steering wheel to turn the wheels and to steer the vehicle.The steering can be assisted hydraulically or electrically to reduce thesteering forces for the rider.

In the second category of such ATV's, the vehicles are skid steered andhave no horizontal pivoting wheels. All wheels are solid mountedregarding the driving direction of the vehicle and are rigidly connectedto a suspension system or directly to the vehicle body. This applies forwheel driven vehicles either with 4, 6, or 8 wheels as in FIG. 2, or forvehicles with endless tracks instead of wheels. The present inventionpertains to this second category.

Such skid steered ATV's are known from different manufacturers indifferent vehicle classes, beginning with the very heavy battle tanksand ending with light vehicles with a weight of about 1 ton at maximum,passing by the commercial snow handling vehicles and the vehicles areused in the construction and the like.

The present invention pertains to a sector out of all possible skidsteered vehicles, such as the full track ATV as disclosed in the U.S.Pat. No. 7,131,507 to the same applicant or light weight small vehicleswith four, six or eight wheels, which are present on the market. Thedryweight of those vehicles is under about one ton.

One of the drawbacks of the known ATV's of the prior art, also of thelow weight ATV, in the following LATV, concerns the steering, inparticular if smooth control and full security is requested at highervehicle speeds and expecially at variable or changing ground conditions.

These light and relatively small LATV are usually steered in a way, thatthe drive system is divided into the right wheels or track and into theleft wheels or track, and that if steering is applied, the left or theright wheel group ( or track) is disconnected from the drive with somekind of a clutch, and a brake force is applied to that same wheel groupor track to slow down the speed and to make the vehicle turning becauseof this resulting speed difference of the wheel groups or tracks of thevehicle.

The drawback of such systems is, that the brake which is needed to steerthe vehicle is destroying torque on the one side of the vehicle, e.g.the inner side of the vehicle, while driving a curve, whereas on theother side of the vehicle, the outer side, more torque and track speedis needed to keep the vehicle speed constant. This system is inefficientand does not allow operating the vehicle smooth and safely at higherspeeds, especially if the driving ground condition is changing from hardto soft resp. from tar to snow or mud, while driving around a cornerwhere these vehicles are getting out of control because the driver mustadapt the applied braking forces during such changes of conditions tocompensate for the higher or lower grip and resistance behaviour of thetracks or wheels, which is practically not controllable because of thevery short reaction time involved.

To obviate the above mentioned drawback, it is known to use adifferential steering device. There exist very heavy and verycomplicated differential steering systems for battle tanks and the likeheavy vehicles, but these cannot be used in light and small vehiclesbecause of complexity, weight, size and costs, as per the followingexamples:

U.S. Pat. No. 6,135,220 discloses a track-laying vehicle and is directedto a modular system for supporting the drive mechanism. This systemcomprises two drive units including a differential and a steeringassembly using an additional differential.

U.S. Pat. No. 4,434,680 discloses a steering differential forearthmoving tractors, but this steering differential is not applicablefor fast moving LATV and too complex for light and low cost vehicles.

WO 97/02975 discloses a differential driving system with twodifferentials and a steering differential.

SUMMARY OF THE INVENTION

It is in the light of the above mentioned prior art an object of thepresent invention to provide for an effectful but yet simple and easy toproduce differential steering device for skid steered LATV's, enablingto drive and steer in a controlled manner at higher vehicle speeds withhigh safety and smoothness even if the ground surface condition ischanging dramatically while driving fast around a corner.

This object is attained with a differential steering device, wherein theATV is a light ATV (LATV) and wherein the differential steering deviceis designed to produce a defined differential speed of the two driveunits of the vehicle related to the steering angle of the steeringdevice regardless to the surface condition on which the vehicle isdriving, whereby an additional steering drive acts on the differentialgear.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages will become clear from thedetailed description which follows with reference to the drawings.

FIG. 1 shows a simplified perspective view of a full track LATVaccording to the prior art,

FIG. 2 shows a simplified lateral view of a wheeled LATV according tothe prior art,

FIG. 2A shows the LATV of FIG. 2 in an elevational view,

FIG. 3 shows a simplified elevational view of the driving components ofa vehicle according to the invention,

FIG. 4 shows schematically a differential steering device according tothe invention,

FIG. 5 shows a hydraulic steering unit according to the invention, and

FIG. 6 shows a simplified schema of an electronic throttle.

DETAILED DESCRIPTION OF THE INVENTION

As will be explained in detail below the new differential steeringsystem principle can be used on either wheel or track driven skid steervehicles, allows to control the vehicle safely also at high speeds, upto over 60 mph, and keeps the vehicle on track even if the drivingsurface changes dramatically from tar to snow or mud during steering thevehicle around a corner.

The base of the new system works in a way that the driving power isproduced with a combustion engine, which is connected over a gearboxwith a shaft or directly to the differential steering gear case. Theexact configuration of the drive- and steering unit is not relevant, andhow this is designed; it could be for example executed electrical,hydraulic, and mechanical or as a combination of those.

If the vehicle is driving straight forward, the power is applied toeither both wheel groups or tracks on each side right and left of thevehicle drive units, both drive units turn exactly at the same speed,regardless of the needed torque of each side, depending on the drivingsurface conditions. For example, if the vehicle is on snow or mud, softand slippery surface on the one side, and on concrete or tar, hardsurface, on the other side.

If the vehicle steers to one side, the steering system located in thesteering gear case applies a differential speed to the driving speeds ofeach drive units, initiated by a hydraulic system and the differentialgears. The speed of the right and the left drive unit is differentdepending on the desired corner radius the vehicle is driven.

The differential speed of the two driving units is achieved by acontrolled variation of the drive ratio between the two driving units,and not by applying any steering brakes and therefore not destroying thedriving power. The total torque applied to the drive systems does notchange during steering; only the distribution of the torque is changing.The torque reduced on the one side is applied/added to the other side.Based on this behavior, the vehicle keeps a constant driving speedduring steering without any additional power supplied to the drive unitsto compensate for steer-braking losses.

The electronic throttle control system which will be explained belowjust compensates for the additional power needed for hydraulic system toinitiate the steering input. This system allows to control thedrivability of the vehicle for smooth and easy riding, also being ableto control the vehicle speed limitations for either different drivingmodes i.e. learner mode, or just to achieve safety while driving thevehicle smoothly reverse with a limited vehicle speed controlled by theelectronic throttle instead of any hard engine reverse limiter. The samefunction can be applied to other gear stages i.e. to protect the enginefrom overreacting in short gearing ratios.

The steering input is effectuated by a handlebar in the present case,but can be effectuated by a steering wheel, or even by a servo forremote control of the vehicle. The steering angle of this steering inputdevice defines the differential speed of the two drive units of thevehicle and therefore the turning radius of the vehicle depending on thevehicle speed; and this regardless of the various grip conditions on thetwo drive units.

Due to the layout of the steering system, the steering result depends onthe vehicle speed in a degressive way, thus that at low vehicle speeds,the steering input results in a higher differential speed ratio of thedrive units, and therefore in a smaller turning radius of the vehicle.

At higher vehicle speeds the same steering input results in a lowerdifferential speed ratio of the drive units and therefore in a widerturning radius. This degressive behavior allows a high maneuverabilityof the vehicle at low speeds but gives a smooth and safe reaction athigh speeds. Such behavior is also known from the automotiveapplications where this is also a big concern.

If during steering, the ground surface is changing, the system balancesthe torque needed on each side and keeps the same differential speedratio as the steering input demands. This behavior of the steeringsystem is most advantageous and helps to steer the vehicle safe andprecisely also at higher vehicle speeds and on various or changingground surface conditions.

FIG. 1 shows a simplified perspective view of a full track LATVaccording to the prior art, where the two tracks 50 are supported by theidler wheels 51 which are mounted to the suspension arms. The straddletype seat 53 has the capacity for one or two persons, one behind theother, the driver controlling the vehicle with a motorcycle typehandlebar 52.

FIG. 2 shows a simplified perspective view of a wheeled LATV accordingto the prior art, where the wheels 55 are mounted usually directly atthe carosserie 54. The seat 56 also offers place for two persons butside by side, the driver controlling the vehicle through the steeringlevers 57 by pulling one lever to the back for turning the vehicle tothe corresponding side.

FIG. 3 shows a simplified elevational view of a vehicle according to theinvention, wherein the engine 1, which is an internal combustiongasoline engine in this case, delivers the power through a variabletransmission 2 and a switching gearbox 3 for selection of the positionfast forward, low gear, neutral, reverse and parking. The engine couldalso be a diesel or any other kind of power plant. This present gearboxassembly is a manual shifted gearbox, which also could be an automaticgearbox, or any other kind of clutch and transmission includinghydrostatic drive. The gearbox 3 is linked to the drive shaft 4 whichbrings the power to the differential gearbox 5 in the back of thevehicle. The output of the differential gearbox is connected with thefinal drive shafts 6 and the brake 7 on both sides and delivers thepower to the tracks 51 on each side of the vehicle. The engine alsodrives the hydraulic pump 9 which feeds the hydraulic steering motor 8in case of a steering input of the driver according to the functionaldescription in FIG. 5. This present layout of the components is anexample how the system can be executed according the U.S. Pat. No.7,131,507 to the same applicant. In this context, the exact layout isnot important, the engine and also the steering gearbox could bearranged differently, resulting in the same functionality of the system.

FIG. 4 shows schematically a differential steering device according tothe invention, wherein the power from the engine goes to a coupler 11and the input shaft 10 to the angle gear and gear reduction unit 15. Thedriven gear reduction unit 15 is rigidly connected to the differentialgear input shaft 16 on both sides and delivers the power to the inputgear 19 of the differential gearbox 14, which are planetary gear sets inthis case. The differential gears could also be executed as angle gearsets or any other kind of gearbox layouts. The input in this case iseffected on the sun gear 19 of the planetary gear set, but could also beeffected on either the planetary gear or the ring gear in anyconfiguration of input/output having the gear ratio's adapted dependingon the system.

In the present layout, the power output is directed from the ring gear12 over the output shaft 20 and the connection flange 13. The steeringinput is directed from the hydraulic steering motor 8 through the gearsand shafts 23, 24, 25, 22, to the planetary gear support 21 and theplanetary gears. While driving the vehicle straight in either theforward or the reverse direction, without any steering input, all thesecomponents are standing still, which results in a fixed ratio of thedifferential gears with the same output speed on both sides. Both tracks51 are therefore rigidly connected for maximum traction.

When a steering input is applied from the driver, the differential gearsget driven from the steering system as is for example described indetail in FIG. 5 below. Depending on the amount of steering, thehydraulic motor 8 drives faster or slower in the one or the otherdirection regarding the turning direction requested, and drives theplanetary gear supports 21 through the gears and shafts 23, 24, 22, 25.The planetary gear support 21 moves the planetary gears 17 through theshaft 18 which changes the ratio of the planetary gearset between thesungear 19 and the ringgear 12 and results in the differential speed ofthe two output shafts 20. To keep a constant velocity of the vehicle,the outer side output shaft 20 and drive unit need to run faster thanthe neutral vehicle speed, the other side output shaft for the sameamount slower, which is achieved by inverting the rotational directionof the planetary gear support of the one side by the intermediate shaft25 to change the ratio of the planetary gearset either into positive ornegative.

Within this system, the drive of the hydraulic steering motor 8 resultsin the two opposite rotating planetary supports and therefore in lower,respectively higher drive ratio's of the output shafts 20 and the finaldrives 13 in regard to the rotating speed of the input shaft 10. A bigadvantage of this system also results of the fact, that the steeringdrive input r.p.m. range of the planetary support 21 get's overlaid bythe vehicle drive r.p.m. range of the differential gear input shaft 16,which results in a differential speed of the final drives 13 dependingon the vehicle speed. As a result, the turning radius gets wider withincreasing vehicle speed at the same steering input from the handlebar52. This degressive steering behavior is most advantageous and allowscontrolling the vehicle safely at high vehicle speeds, but also allowsthe best maneuverability at low vehicle speeds.

Another big advantage of this system is, that both final drives 13 arealways's linked together over this variable ratio, assuring that thevehicle moves safe and smooth in any kind of conditions of the drivingsurface and driving resistances, without any influence of how muchtorque is applied from the driver.

It follows that the input drive shaft 10 is rigidly connected throughthe shaft 16 to the two differential gears, any kind, one on each side.The outputs of these differential gears are rigidly connected on eachside to the drive shaft 6 of the wheels or tracks.

If the vehicle drives straight without any steering input, theadditional hydraulic steering motor 8, axle and gears 2, 4 are stoppedand both driven wheels and tracks are therefore fixedly connected witheach other and the input drive shaft 6. In this case, the drive train ispurely mechanical without any additional losses.

If a steering input is applied to motor 8, the motor starts to turn inthe one direction depending on the steering input, left or right. Ther.p.m. range of this motor is depending on the steering angle of thesteering input.

On the action of the shaft and gears 2, this also could be for example abelt drive, the differential gears starts to turn, which results in adifferential speed of the output shafts 20 on both sides. Due to thefact that one wheel or track needs to turn faster than the other, or asin the still standing case, when turning on place, one shaft drivesforward and one backwards, the steering drive train needs the axle andgears 4 to change the rotating direction of the one drive side of thedifferential gearbox.

FIG. 5 shows a steering hydraulic system according to the invention,wherein the combustion engine 1 drives a hydraulic pump 9 through a sidedrive to produce hydraulic pressure needed for the steering function. Inthe present case, the combustion engine 1 also drives the vehicle,which, however, is not important for the functionality of the system.The hydraulic pump 9 also could be driven by a separate electric motorfor example. The valve 27 controls the operating pressure and limits themaximum system pressure for safety.

The priority flow control valve 28 controls the flow volume to thesteering valve 29 in such a way that the pressure drop over the steeringvalve is used as a control pressure difference. The priority controlvalve 28 works in this layout as a pressure balance and fulfills thefunction of a 3 way flow control valve. It therefore increases ordecreases the volume to the steering valve 29 thus, that the controlpressure difference remains constant all the time. The control pressuredifference is switched with the valve 30 either to the one or to theother flow direction in the hydraulic circuit. In the present system,this valve is integrated in steering valve 29.

The steering valve 29 acts on the one hand like a adjustable orifice andon the other hand it controls the flow direction over the hydraulicsteering motor 8 to achieve the forward or reverse rotation depending onthe steering input of the driver to turn the vehicle to the one or theother side.

With this configuration, the result lies in a constant relationship ofthe volume flow and open cross sectional area and therefore in a relatedr.p.m. range of the hydraulic steering motor 8, independent of thecurrent system pressure and flow volume delivered from the hydraulicpump 9.

The amount of oil which is not used for the steering to achieve thedrivers steering input can be either used to drive any working hydraulicunits 31 or will be returned over a return line 39 with heat exchanger35 and filter 36 back in the oil tank 37. The oil tank is vented througha cap 28 to prevent under/over pressure in the tank.

The steering remains working constantly, independently of the pressureused for the working hydraulic unit which is controlled over the flowcontrol valve 32 and the system pressure control valve 27. If there isnot enough volume flow available depending on the operating r.p.m. rangeof the combustion engine 1 and the pump 9 to fulfill the needs of thesteering requests, the steering always has priority because of thefunction of the priority valve 28. In such a case, the working hydraulicjust gets the oil which is not needed for the steering function.

To obtain a steering force feedback to the driver through the handlebaror any other steering device, an optional hydraulic cylinder 33 can beadded into the feedlines of the hydraulic steering motor 8. Thisfeedback force is relative to the pressure needed in the steering systemand therefore an indicator for the traction of the two tracks or wheelsof the vehicle.

The 4-2 valve 34 is used to reverse the rotation of the hydraulicsteering motor 8 and therefore to keep the steering input directionindependent of forward or reverse movement of the vehicle. This valve 34can be switched electrically, hydraulically or mechanically, always inthe default position for forward driving due to safety reasons.

FIG. 6 shows a simplified version of an electronic throttle controlaccording to the present invention to control the engine torque anddrivability of the vehicle. In the prior art ATV's, the torque of theengine is controlled mechanically via a throttle cable, an input devicein form of a throttle pedal 42A or a thumb throttle lever 42 which opensand closes the throttle body of a combustion engine to control therequired torque to drive the vehicle.

An input device in form of a throttle pedal 42A or a thumb throttlelever 42 is supplying an electronic signal to the electronic throttlecontrol (ETC) unit 41. This control unit 41 can be integrated in theengine control unit to control the combustion engine fuel, ignition,etc.

Due to the fact that even a skid steered vehicle according to thepresent invention uses some power increase for steering the vehicle, theengine needs to deliver some more torque to warrant a stable drivingwithout any corrections made by the driver of the vehicle to allow asafe driving.

According to the present invention, the steering is initiated by ahydraulic system, which controls the differential speed of the tracks orwheels to let the vehicle steer in a direction. As explained in thehydraulic system, the combustion engine 1 with its power take off 49 isdriving a hydraulic pump 9 where the hydraulic oil is supplied to thepump via the feed line 46 to the pump and from there via the pressureline 47 to the pressure sensor 48. The priority valve 28 defines thepressure of the hydraulic system needed to generate the requireddifferential speed driven by the hydraulic steering motor 8, see FIG. 5.

The needed torque for steering is mainly depending on the surfaceconditions on which the vehicle is driving. On hard surfaces like tar orconcrete, more torque and therefore a higher hydraulic pressure isneeded to let the vehicle skid steer as requested from the driver. Onsoft surfaces like mud, sand or snow, less torque is needed to reach thesame steering amount and radius of the vehicle. But also the drive trainratio, set by the transmission is influencing the system in the sameway. Choosing a short ratio in low gear needs less torque from theengine then using a long ratio in high gear to drive the vehicle.

To compensate this torque absorbed from the engine and to allow anautomated stable vehicle driving, the pressure sensor 48 measures thehydraulic pressure generated and reports this value to the ETC controlunit 41. The ETC has integrated models and maps to calculate the desiredthrottle opening compensation and supplies this information to thethrottle actuator 45. This throttle actuator changes the throttle body43 opening over an axle 44 to open one or more throttles. Depending onthe application this can be one or more throttles for all cylinders orindividual throttles for each cylinder; the present application showsindividual throttles per cylinder, synchronized according to the amountof the needed torque, reflected in more throttle % opening.

The amount of this compensation is calculated from the pressure inputvalue of the pressure sensor 48 as a base function depending on thevehicle speed. To adapt to the various possible situations, additionalcompensation functions are needed for a stable function of the system.In the present invention, vehicle speed, engine r.p.m. range, engineload, gear position and hydraulic oil temperature are used to calculatethe final correction percentage of the throttle opening, also enginetorque, based on three-dimensional map tables or two-dimensional tables,which also can be calculated model functions as often used in thetoday's automotive applications of similar systems of electronicthrottle control systems.

In addition to the main function of the ETC system in skid steeredvehicles—compensating for steering losses—other functions as optimizeddrivability, learner mode with reduced engine power and limited vehiclespeed, smooth and safe vehicle speed limiting depending on the gearchosen, remote control while unmanned driving or engine power control towork with additional hydraulic equipment 31, see FIG. 5, can be realizedsafely without any additional electronic equipment.

1. A skid steered all terrain vehicle (ATV), comprising two drivingunits for the wheels or tracks on both sides of the vehicle and adifferential steering device with a differential gear, wherein the ATVis a light ATV (LATV) and wherein the differential steering device isdesigned to produce a defined differential speed of the two drive unitsof the vehicle related to the steering angle of the steering deviceregardless to the surface condition on which the vehicle is driving,whereby an additional steering drive acts on the differential gear. 2.The LATV according to claim 1, wherein the differential steering deviceproduces a differential speed of the two driving units which isdepending on the steering device input thus, that when turning thevehicle, its radius is smaller at low vehicle speed than at high vehiclespeed while having the same steering input.
 3. The LATV according toclaim 1, wherein the drive engine and the gearbox are longitudinallymounted side by side in the front section of the vehicle and thecontinuous variable transmission is mounted on the front of those units.4. The LATV according to claim 1, wherein the differential steeringdevice is mounted in the rear section of the vehicle aligned with thedrive axles of the two driving units.
 5. The LATV of claim 1, whereinits dry weight is less than about one ton, its length less than about3.5 m and its width less than about 1.65 m.
 6. The LATV according toclaim 1, wherein the differential steering device comprises a gear traincomprising a steering motor acting on a zero shaft connected to suncarriers for working with sun wheels which in turn are connected to theengine motor, whereby the sun gears acts with ring gears connected tothe connection flanges of the drive units.
 7. The LATV of claim 6,whereby the zero shaft is connected directly to one sun carrier and tothe other sun carrier via an intermediate shaft for inversing thedirection.
 8. The LATV of claim 1, wherein the driving engine is aninternal combustion engine, or an electrical motor.
 9. The LATV of claim1, wherein the steering motor is a hydraulic motor or an electricalmotor.
 10. A skid steered all terrain vehicle (ATV), comprising twodriving units for the wheels or tracks on both sides of the vehicle anda hydraulic steering device comprising a hydraulic pump and a hydraulicsteering motor, wherein the ATV is a light ATV (LATV) and wherein thehydraulic circuit comprises a priority current control valve controllinga steering valve connected to the hydraulic steering motor.
 11. The LATVof claim 10, wherein its dry weight is less than about one ton, itslength less than about 3.5 m and its width less than about 1.65 m. 12.The LATV of claim 10, wherein the priority current control valve worksas pressure difference control valve and controls the amount of oilflowing to the hydraulic steering motor independent of the hydraulicsystem pressure.
 13. The LATV of claim 10, wherein the hydraulic circuitfurther comprises a pressure limiting valve.
 14. The LATV of claim 10,wherein a hydraulic valve is used to change the direction of thehydraulic oil flow depending if the forward or reverse gear is engaged.15. The LATV of claim 10, wherein the hydraulic pump for the steeringand for the auxiliary drive is mounted on the engine housing and isdirectly driven from the crankshaft of the combustion engine.
 16. TheLATV of claim 10, wherein the circuit further comprises an auxiliaryworking hydraulic system, and the hydraulic steering motor system isdesigned thus, that is has always priority over the auxiliary workinghydraulic system.
 17. The LATV of claim 10, wherein the hydraulicsteering motor acts on the differential gear of claim
 2. 18. A skidsteered all terrain vehicle (ATV), comprising two driving units for thewheels or tracks on both sides of the vehicle, wherein the ATV is alight ATV (LATV) comprising an engine torque controlling device with anelectronic throttle control system connected to the engine and to thedriver throttle lever or pedal.
 19. The LATV of claim 18, wherein theelectronic throttle control system compensates the torque needed forsteering efforts in accordance to a steering pressure sensor valuecontrolling the electronic throttle and thus compensating the enginetorque.
 20. The LATV of claim 18, wherein the electronic throttlecontrol system is designed to compensate the torque needed for steeringefforts for assuring that the engine is keeping its r.p.m. range stableduring steering without driver input on the driver throttle or pedal.21. The LATV of claim 18, wherein the electronic throttle control systemis designed to control the maximum vehicle speed differently dependingon the gear engaged, without engine r.p.m. range limiting.
 22. The LATVof claim 18, wherein the electronic throttle control system is designedto provide a learner mode where the vehicle speed can be adjusteddepending the rider skills.
 23. The LATV of claim 18, wherein its dryweight is less than about one ton, its length less than about 3.5 m andits width less than about 1.65 m.
 24. A LATV according to claim 1,wherein the differential steering device, the hydraulic steering deviceand the torque compensating device enables the LATV to turn on the spotand to drive very tight curves.
 25. A LATV according to claim 10,wherein the differential steering device, the hydraulic steering deviceand the torque compensating device enables the LATV to turn on the spotand to drive very tight curves.
 26. A LATV according to claim 18,wherein the differential steering device, the hydraulic steering deviceand the torque compensating device enables the LATV to turn on the spotand to drive very tight curves.